This invention pertains to the art of brake systems for heavy vehicles, and more particularly to an air brake system that satisfies recent standards imposed with regard to emergency brake performance. It will be appreciated that as a result of the modifications taught by the present invention, the air brake systems can now meet new emergency stopping distance requirements with a failed rear axle service control line.
In presently available truck brake systems, depressing a foot pedal or treadle actuates a foot control valve to actuate air brakes associated with the wheels. Dual supply ports and dual delivery ports are provided with the foot control valve in order to achieve desired front and rear braking. In systems of this type, a relay valve is associated with the rear wheels. The relay valve includes a supply port that communicates with a source of compressed air and an exhaust port that communicates with ambient or atmosphere. A delivery port is in operative communication with the wheel brake actuators to effect desired braking. In addition, and in accordance with known systems, a service port of the service relay valve receives a control signal (e.g. pneumatic pressure) from the foot control valve. When the foot control valve is actuated by depressing the foot pedal, pressurized air is delivered to the service port. This, in turn, pressurizes a movable piston that actuates an inlet/exhaust valve in the relay valve to establish communication between the supply port and the delivery port to effect braking.
Recent revisions in the national standards require that a safe stopping distance be achieved with a failed rear axle service control line, i.e., if the service line from the foot control valve to the relay valve is insufficient, inoperative, etc. then the brake system still must satisfy the emergency stopping distance requirements.
It is also preferred that modifications to existing systems be minimized so that proven designs and components can be used.
Accordingly, a need exists for an effective, simple, and economical solution.